Request Interceptor

What is @networkoptix/request-intereptor?

This package allows intercepting request and applying middleware that can modify the request before it is handled by the browser/node or to modify a response before it's return back to the application.

What can it do?

The RequestInterceptor class handles handles registering middleware that intercepts requests and responses.

The middleware classes are all derived from the RequestMiddleware class. They can be configured to handle requests, responses, or both.

The middleware applied to the requests/reponses in the order that they are declared.

Usage

The RequestInterceptor class exposes a register static method which is used to initialize the interceptor. This method accepts an array of RequestMiddleware to apply to requests/responses.

Middleware

Included in the package are abstract and concrete classes for handling common use cases.

Generally concrete class names start with the word With to make it clear if it's an abstract or concrete class. So SomeMiddleware would be an abstract class and WithAnotherMiddleware would be a concrete class.

Abstract Middleware

An example abstract middleware class would be the AuthenticationMiddleware which defines shouldAuthenticate and authenticate classes and simplifies creating concrete middleware that handles various authentication schemes.

Concrete Middleware

An example abstract middleware class would be the WithBearerMiddleware which defines specific implementation of the shouldAuthenticate and authenticate methods to handle bearer token authentication.

Nx Meta Middleware

The Nx Meta middleware are specialized for interacting with Nx Meta services. These middleware classes will start with either Nx for abstract classes or WithNx for concrete classes.

Example of creating custom middleware from abstract class:

import { AuthenticationMiddleware } from '@networkoptix/request-interceptor'

export class WithBearerMiddleware extends AuthenticationMiddleware {
    async authenticate(request: Request): Promise<void> {
        request.headers.set('authorization', `Bearer ${await this.getToken()}`);
    }

    constructor(
        private getToken: (request?: Request) => string | Promise<string>,
        protected shouldAuthenticate: (request?: Request) => boolean
    ) {
        super();
    }
}

Example usage of concrete middleware:

The interceptor should be registered as early in the application lifecycle as possible.

For most applications it would be included in a main.ts or main.js file or a polyfills file.

import { WithBearerMiddleware, RequestInterceptor } from '@networkoptix/request-interceptor'

import { getToken, shouldAuthenticate } './from-other-module'

const middlewares = [
  new WithBearerMiddleware(getToken, shouldAuthenticate)
]

RequestInterceptor.register(middlewares)